This invention concerns clothes washing machines and more particularly such machines in which resettable pressure switches are utilized for sensing and controlling the water level during filling of the tub and basket at the beginning of each wash or rinse cycle.
A common approach in providing automatic control over the fill level of washing machines has involved the use of a pressure-sensitive switch, such as a diaphragm-spring combination which acts to sense the water pressure in the bottom of the washing machine tub. Upon achieving a certain predetermined level of water in the tub corresponding to the adjusted setting of the pressure-sensitive switch, the sensing of the corresponding pressure level causes a solenoid-operated fill valve to be shut off, thus accurately determining the level of water added to the machine.
Some washing machines include recirculation pumps which circulate a portion of the tub water through the lint filter during washing cycles, which cause water level variations in the tub during recirculation. The agitation cycle also causes variations in the water level within the tub during the cycle and it is therefore necessary to prevent the pressure-sensitive switch from falsely activating the fill valve, causing more water to be added to the tub during the wash or rinse cycles.
In many designs, the pressure-sensitive switch has been designed to be "resettable" in that the pressure head sensed must drop down to a predetermined low level in order to again open the solenoid-operated fill valve. The pressure-sensitive switch cannot then be falsely activated and will not again be responsive to pressure head levels until after the tub water level has been reduced at the end of either the wash or rinse cycle. This thereby prevents variations in tub water level from causing such false opening of the fill valve during the wash or rinse cycle.
While the use of a resetting pressure-sensitive switch is generally satisfactory, a problem may arise in recirculation systems, where extremely low tub water levels may occur. Particularly, such a situation may arise in those systems which allow for adjustable water levels as an economy measure. When low water levels are selected, recirculation of water from the tub can result in water levels in the tub declining to the point where the pressure-sensitive switch is reset and thus causes a false operation of the fill valve to add water during the wash or rinse cycle.
Most modern washing machine designs include an outer tub which receives a perforated clothes receiving basket, an agitator within the basket being agitated during washing or rinsing and the basket spun during the extract cycle with the water passing out through the perforate basket and received into the outer tub. The water collected in the tub is caused to be pumped to a plumbing drain through a drain located at the bottom of the tub. Since the basket is perforated, the water level is the same in tub and basket.
It has been recognized that since the volume of water between the tub and basket does not perform a useful washing function, a recirculation system could allow the use of lesser volumes of water for a given wash load. This could be achieved by providing a limited number of perforations in the basket located in the lower region thereof to insure equalized levels during the fill cycle and causing a recirculation pump to pump water emptying through the basket bottom perforations into the tub back into the basket during the wash and rinse cycles. The water level in the tub is thereby reduced to be substantially below that in the basket. This in effect results in a lesser volume of water being required for a given clothes load size. Examples of such systems are found in U.S. Pat. Nos. 3,014,358 and 3,153,924.
In these systems, as well as in the lint removal recirculation washing machines described above, the recirculation pumps generally operate whenever the washing machine motor is being driven and thus for relatively low selected water levels, the recirculation pump may reduce the water level in the tub to a point where the pressure-sensitive switch is reset to thus again cause the false operation of the fill valve and result in water being added unnecessarily.
While there is generally always a slight level of water above the level at which the pressure-sensitive switch tap is located, pressure-sensitive switches which can reliably distinguish pressure head differences at such low levels cannot be produced at reasonably low costs.
It is accordingly an object of the present invention to provide a reliable arrangement for insuring that the water level in the tub above the point at which the pressure-sensitive switch senses the pressure level will always be sufficient to insure that the pressure sensor will not reset. The pressure-sensitive switch will not thereby be reset even if the recirculation pump reduces the water level in the tub to the lowest flow level of the intake into the recirculation pump inlet.
It is a further object of the present invention to provide such an arrangement which does not require extensive redesign of the washing machine components and which may be simply and inexpensively added to the washing machine.